Solve for f 3f+9

$3 f + 9 < 21$

Move all terms not containing $f$ to the right side of the inequality.

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Subtract $9$ from both sides of the inequality.

$3 f < 21 - 9$

Subtract $9$ from $21$ .

$3 f < 12$

Divide each term by $3$ and simplify.

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Divide each term in $3 f < 12$ by $3$ .

$\frac{3 f}{3} < \frac{12}{3}$

Cancel the common factor of $3$ .

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Cancel the common factor.

$\frac{3 f}{3} < \frac{12}{3}$

Divide $f$ by $1$ .

$f < \frac{12}{3}$

Divide $12$ by $3$ .

$f < 4$

The result can be shown in multiple forms.

Inequality Form:

$f < 4$

Interval Notation:

$(- \infty, 4)$

Solve for f 3f+9<21

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